1. Field of the Invention
This application relates to minimally invasive surgical procedures, and more particularly to replacing an intervertebral disc of a patient with a prosthetic device.
2. Description of the Related Art
Chronic back pain can have any of a number of causes or a combination of causes. For example, acute damage to and/or progressive degeneration of a disc, which is located in the interbody space defined between adjacent vertebrae, can lead to pain as the load-bearing and flexibility providing functions of the disc are no longer effectively performed. A number of treatments have been proposed for this condition. Fusion is a procedure whereby a graft intended to promote bone growth within the interbody space replaces some or all of the material in the interbody space. The bone growth causes the adjacent vertebrae to be joined together, after which the two vertebrae essentially become one and flexibility is eliminated. Fixation is another common treatment which involves attaching a structural assembly across two adjacent vertebrae to physically join the vertebrae together to prevent relative motion of the two vertebrae with respect to each other. While these approaches can reduce the pain associated with disc conditions, the substantial reduction or complete elimination of flexibility at the problem disc can lead to greater stress on adjacent discs and other spine problems.
Traditionally, these and other spine treatments have been performed by way of open surgery. In open surgery, the surgeon typically makes one ore more large incisions and cuts and/or strips muscle tissue surrounding the spine in order to access the vertebrae. Because the amount of tissue exposed is so great, care must be taken not to injure nerve tissue in the area. Consequently, these traditional surgical procedures carry high risks of scarring, pain, significant blood loss, and extended recovery times.
Apparatuses for performing minimally invasive techniques have been proposed to reduce the trauma of spine surgery by reducing the size of the incision and the degree of muscle stripping in order to access the vertebrae. One such apparatus provides a constant diameter cannula which is made narrow in order to provide a small entry profile. As a result, the cannula provides minimal space for the physician to observe the body structures and manipulate surgical instruments in order to perform the required procedures. A narrow cannula is typically too small to perform most spine procedures. Accordingly, several cannula are required to perform even the simplest procedure.